Hi I like your last paragraph Brian - I think this is closer to the truth. Tektite glass doesn't survive 35 million years unless it is in rather special preservational conditions. The U-grooved specimens likely sat around for a few hundreds of thousands of years in an acidic (rainwater) environment which etched them. Had they remained in this environment they would be gone by now. Instead they were incorporated into a sediment that, for whatever reason, preserved them. I'm not familiar with the Manning Fm and Jackson Fm. Low permeability would preserve specimens. Also if there was only acid leaching then the alkaline ions are removed and then the remaining silica acts as a barrier and the process stops (Adams, 1984). Similarly if there is only alkaline attack in a closed environment then waters become saturated in silica and the etching essentiallys stops. One wonders whether the rock was saturated in silica, suppressing the leaching rate to zero?
As Brian mentioned it's also noteworthy that some bediasites also show pyramidal v-grooving, which is caused by alkaline etching attacking the silica network. Some show the classic u-grooving like the philippinites. The u-grooving and navels are chemically enhanced cracks formed when the tektite cooled rapidly and spalled in the latter stages of re-entry. I have philippinites that show paper-thin cracks, narrow u-grooves and thick u-grooves - every stage. Regards, Aubrey Whymark www.tektites.co.uk ----- Original Message ----- From: Steve Dunklee <[email protected]> To: [email protected]; brian burrer <[email protected]> Cc: Sent: Saturday, 25 February 2012, 2:04 Subject: Re: [meteorite-list] Bediasites agree with Steve's unproven tektite theory Imagine? outgasing causes a spike to form on the surface of a tektite as it cools 5 miles up. then as it falls the spike breaks off to form a ring at its base. half ring or u groove ect. cheers Steve --- On Fri, 2/24/12, brian burrer <[email protected]> wrote: > From: brian burrer <[email protected]> > Subject: [meteorite-list] Bediasites agree with Steve's unproven tektite > theory > To: [email protected] > Date: Friday, February 24, 2012, 9:49 PM > Hi list, > > Bediasites are well known for, among other things, these two > traits: > > 1.Most Bediasites show ample evidence of abrasive transport > and minor > to severe smoothing of the surface. > > 2.Bediasites are found in/on the basal portion of the > Manning unit of > the Jackson formation in Texas. They are almost never > encountered > "off formation". The age of volcanic ash later/higher > in the Manning > is about one million years after Bediasite formation so the > tektites > were placed there rather soon after the event. > > The age of deposition of the Bediasites in the Manning would > be about > thirty five million years ago. Despite the passing of > an immense > amount of time etching has failed to significantly alter the > surfaces > of the tektites. U-grooves, V-grooves and navels all > exist on stones > with different amounts of ancient abrasion only slightly > muting some > and almost obliterating others. If they were in an > environment > conducive to etching after burial Bediasites should all be > similar to > the Besednice hedgehog Moldavites. The evidence > suggests that little > etching has occurred on most Bediasites after transport. > > These things taken together suggest that surface sculpture > on > Bediasites was a pre-existing condtion and was not developed > by later > etching. > > There is one small problem with this; the tektites did get > some amount > of time (less than one million years) to etch prior to their > addition > to the basal Manning sediments. While it is possible > they were > heavily etched in their earliest years and then abrasively > transported, it is certain they did not etch significantly > once > buried. > > > > Happy hunting, > Brian > ______________________________________________ > > Visit the Archives at > http://www.meteoritecentral.com/mailing-list-archives.html > Meteorite-list mailing list > [email protected] > http://six.pairlist.net/mailman/listinfo/meteorite-list > ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
